1. Field of the Invention
This invention relates to an image processing apparatus usable in various image handling equipments such as dot matrix printers or laser beam printers.
2. Description of the Prior Art
Recently, dot matrix printers or laser beam printers have been widely used. U.S. Pat. No. 4,847,641 discloses piecewise print image enhancement for dot matrix printers.
In an apparatus of U.S. Pat. No. 4,847,641, a print enhancement circuitry to enhance the printed image produced by a laser beam printer is interposed between the character generator circuits and the laser drive circuits to modify the laser drive signals provided by the character generator circuits. Bit data representing successive lines of the bit map for a desired image are stored in a first-in first-out (FIFO) buffer. The bit pattern sample window having a central cell (bit) and a selected (arbitrary) number of neighboring bits is compared to a number of matching bit patterns or templates, each of which is associated with an error element or cell. When a logic matching network detects a match, a modification signal associated with a unique compensation cell (bit) is generated. The sample window central bit is then replaced (modified) with the unique compensation bit required by the matching template. In this way, all bits in a desired bit map, or set of bit maps, are examined and their corresponding laser drive signals are modified to compensate for the errors associated with the matched templates in a piece-wise manner.
The print image enhancement techniques disclosed in U.S. Pat. No. 4,847,641 have the following problem. A large number of templates is necessary for good and reliable enhancement. Thus, the matching network for comparing the sample window bit pattern with the templates tends to be complicated in structure.